The disclosure relates to a photon detector comprising at least one paralyzable photon-sensitive element, wherein the photon-sensitive element can be embodied for example with an SPAD (Single Photon Avalanche Diode). Furthermore, the disclosure relates to a distance measuring device comprising such a photon detector.
Distance measuring devices are known which align a temporally modulated light beam in a direction toward a target object whose distance from the measuring device is intended to be determined, and at least partly detect the light reflected or backscattered from the target object aimed at and use it for determining the distance to be measured. In this case, a typical measurement range is in a range of distances of from a few centimeters up to several hundred meters.
In order to be able to measure the distance from the target object, a propagation time of photons which are emitted from the measuring device toward the target object and are detected in the measuring device after returning can be determined and the desired distance can be determined therefrom. By way of example, short light pulses can be emitted and a propagation time of a light pulse from emission until detection can be measured. Alternatively, a light beam can be temporally modulated in terms of its intensity, for example by means of a periodic modulation of the light intensity, and a phase shift between the emitted and detected light signal can be used to determine the propagation time and thus the distance from the target object. The principle of laser distance measurement is generally known by the designation “time of flight ranging” for example with continuous modulation of the intensity of the laser beam.
In order that the light returning from target object, and in particular the temporal modulation of said light, can be detected well and, if necessary, distinguished from background light, it can be advantageous to use light detectors, which are also designated herein as photon detectors, having specific properties. By way of example, distance measuring devices have been developed in which the returning light is detected with the aid of SPADs. SPADs can enable a very good detection sensitivity through to the detection of individual photons. In contrast to many other light detectors, wherein the output signal is analog and the strength of the output signal is dependent on the incident light intensity, SPADs can provide a digital signal with pulses having substantially the same strength, wherein each pulse indicates the detection of a photon and, consequently, the digital signal supplied by the SPAD reproduces a photon counting rate. One possible advantage of the use of SPADs as light detectors may reside in the fact that SPADs can be produced compatibly with CMOS technology and, consequently, can be integrated cost-effectively for example into an integrated circuit for the evaluation of the measurement signals.
However, it has been observed that distance measuring devices which use SPADs for detecting returning light, particularly in very light-intensive measurement conditions, cannot yield sufficiently reliable measurement results.